British wheel brand Parcours has published results from aero tyre testing some of the newest performance rubber on the road this year. But they’ve gone several steps further than the usual wind tunnel testing to produce results that may be of far higher value.
Parcours also gathered extensive real-world on-bike yaw angle data – collected during the development of its latest aero wheelsets – which provides a unique insight not only into which tyres are fastest across a range of yaw angles, but which yaw angles we are likely to experience in live, outdoor riding and racing environments.
Better yet, they’ve taken all that aero data and combined it with BicycleRollingResistance.com‘s (BRR) roller testing CRR data to give us a ranking of four new, aero-focused tyres and a deeper understanding of what makes a given tyre relatively faster or slower in a variety of conditions.
There are limits to the learnings. Personal testing is still the only way to truly know an individual’s optimal setup. And Parcours tested just five tyres – four new aero-focused tyres in Continental’s Aero 111, Conti’s GP 5000 TT TR, Vittoria’s new Corsa Pro Speed and Schwalbe’s Pro One Aero, plus the new, all-around Pirelli P Zero TLR – on one rim (Parcours’ own Chrono 68, a 68.6 mm deep, with 32mm external and 22.5 mm internal widths), and at high speeds: 48 km/h.
But even with those caveats, Parcours’ endeavours give those unable or unwilling to test a new insight into which tyre to choose and when. A major finding: As we’ll delve into below, the differences between tire aerodynamics are minor at lower yaw angles, but as the wind picks up and the yaw angles with it, the difference in simply changing a tyre is startling. But also: Parcours’ data suggests that the vast majority of our riding time is spent in those lower-yaw conditions. Picking the absolute fastest tyre relies on knowing how much those variables come into play on a ride or race.
Aerocoach has been at the forefront of independent tyre testing in recent years, but its last update came over a year ago following the launch of Vittoria’s new Corsa Pro. Most of the tyres Parcours took to the wind tunnel have all been released in the time since then, and so their data is the first independent look we have on these new tyres.
A dive into the data
Skipping straight to the juicy stuff: Combining the aero drag from Parcours’ yaw-weighted average with the rolling resistance data from BicycleRollingResistance.com to give an overall performance figure for each tyre, the Vittoria Corsa Speed comes out on top by almost 1.5 watts. But there’s plenty more interesting insight to be gleaned from Parcours’ testing, and there are a few reasons you might not choose Vittoria despite its combined-data victory.
Of note: the Corsa Pro Speed has a much lower stall angle than other tires, with drag decreasing initially but then levelling off around 7.5° of yaw, as seen in the graph below. In comparison, even the non-aero-focused Pirelli P-Zero sees its drag decrease until about 12.5° of yaw.
The Continental GP 5000 TT TR is in second place to the Vittoria. The lighter, lower-rolling resistance version of its hugely popular GP 5000 S TR tyre was first introduced as a time trial-day tyre, but teams quickly caught on to its improved performance for use in mass-start racing. Puncture concerns about lightweight TT tyres of yesteryear were quickly quashed given most Conti-equipped teams now race on the TT TR.
Meanwhile, the Aero 111 – a collaboration between Continental, SwissSide and DT Swiss that launched at Eurobike but was conspicuously absent from some pro team partners’ bikes at high-profile time trials this summer – shows essentially no stall angle, with progressively decreasing drag. Continental made similar claims, but Parcours’ data largely confirms it. If Continental’s data are accurate, it’s also much more-stable in handling in those crosswind conditions.
While the individual tyre data is interesting, there’s a deeper question that Parcours starts to address: how relevant is all this to our riding?
The simple answer is very relevant: If you are a time trialist typically choosing between these tyres anyway. Many testers will have used previous iterations of these tyres, sometimes mixing between tyres front and rear, and thus wonder how the new tyres stack up. Are they faster, is the fastest still the fastest, should I still be mixing Conti fronts with Vittoria rears? The data Parcours presents seems to say yes to all those questions.
These are the most important questions for TT riders on TT tyres, but even for riders in other events and situations, the Parcours data throws up plenty more answers and questions if we delve a little deeper.
New understandings of yaw
As tempting as it is to take the ranking and run, the devil is in the yaw angle details here. Before delving into why, it’s important to understand Parcours’ approach to weighted yaw angle. The team at Parcours had spent a lot of time investigating how to collect, analyse, and apply real-world conditions to a controlled test environment in the wind tunnel while developing its latest aero wheels.
As part of this process, yaw was measured using an ultrasonic anemometer, which was attached to 3D-printed brackets on the front and rear wheel axles. Riders were instructed to ride naturally in various wind conditions, on different types of rides, and over varying distances. The tests were conducted over 12 months to capture data across different seasons, and data was collected from the sensors after each ride. While having riders test on their own bikes over this time period could introduce potential errors, it’s also a level of attention to detail and real-world optimisation we don’t see from many brands.
As for the results, Parcours found a significant and consistent difference in yaw angles between the front and rear wheels. On average, the yaw angle at the front wheel was 1.5° higher than at the rear wheel. They also found the riders most often experience yaw angles between 2.5° to 7.5° with yaw angles below 10° representing ~89% of ride time per Parcours’ yaw data.
As relates back to the tyre testing, this yaw angle data is significant.
As Parcours noted in its blog post, there is a distinct difference between the tyres at low and high yaw angles. At low yaw angles – less than 10° – all the tyres tested within just over 2W of each other, with the Aero 111 just one watt faster than the second-place Schwalbe. Parcours also noted that even the slowest tyre, the non-TT or aero-specific Pirelli, may have suffered due to its wider mounted width.
However, at higher yaw angles – 10° and above, and the conditions seen around 10% of the time according to Parcours’ analysis – the differences between tyres are staggering. The Aero 111 was the fastest here – some 17 watts faster than the slowest tyre, the Corsa Speed Pro.
That’s because as the yaw angle increases, the flow over the tyre stalls and detaches from the tyre, and thus, the rim can’t work its aero magic. The best-performing tyres at higher yaw angles not only delay this stall but also aid the flow in re-attaching onto the rim. This not only makes for a faster tyre in these high-yaw scenarios (usually crosswind conditions), but should also translate into increased stability and more predictable handling.
There is of course the question of how often the riders using these performance tyres will see these conditions. It’s a question I put to Dan Bigham for an upcoming episode of the Performance Process podcast. Bigham was confident that even the world’s fastest riders will see high-yaw conditions in the spring Classics or echelon racing. (Yaw angles are typically lower at higher speeds as the relative velocity of any crosswinds is reduced compared to the vehicle’s forward speed. This makes the effect of crosswinds on the yaw angle less pronounced as speed increases.)
But Parcours’ yaw data suggests we mere mortals don’t really see those conditions in the real world, and that’s where we potentially get to the real answers on which tyre you should choose. That answer is: “it depends,” and the only way to know for sure is to test. That said, there a few safe bets you can make:
- If you are riding or racing along a blustery coastline with 30+ km/h winds coming off the sea, as I did recently, you are likely experiencing high-yaw conditions and thus leaning towards the tyres that seemingly perform best in these conditions according to Parcours’ data is probably a good idea. Again, this isn’t just an issue of saving watts; these tyres typically improve handling in these conditions.
- In more typical, low-yaw conditions with a deep wheel like a Parcours Chrono, the Corsa Pro Speed wins in the combined rankings and thus could be the go-to tyre. That said, it stalls relatively early and quite severely around 7.5°. Add in a gust or two as we get closer to those yaw conditions most typically experienced, and the safer bet seems to be either the Continental GP 5000 TT TR or the Schwalbe Pro One Aero.
What we know highlights what we don’t
There’s a lot we still don’t understand here. First up, a question one which poses countless others: Parcours used its Chrono 68 rim for this testing, and so, given that aerodynamics (and, to a lesser extent, rolling resistance) is highly rim-dependent, how would the results vary with similar-depth wheels from other brands, or shallower-depth wheels? That’s not a criticism of Parcours’ testing; the very opposite, in fact. It’s no insult to say Parcours are not the biggest wheel brand, yet they have taken the time and gone to the expense of wind tunnel testing various tyres on their rims to give Parcours Chrono owners (or potential buyers) data to base their tyre selection on. It would be great to see more wheel brands do the same.
Secondly, as already mentioned, plenty of riders are now riding on TT tyres in normal road races. And if we can extrapolate a bit from the data here, that’s a pretty smart move. We don’t have the Vittoria Corsa Pro or Conti GP 5000 S TR data to compare, but taking the new Pirelli P-Zero TLR RS – which according to Parcours was tested because 1) Pirelli don’t currently offer a TT-specific tyre and 2) it’s new, rather than serving as an all-round tyre benchmark against mostly light/low rolling resistance low puncture protection race-day-only tyres – the Corsa Pro Speed offers an almost 6-watt advantage. The GP 5000 TT is five watts faster, and as mentioned earlier it seems plenty resistant to punctures. Would I use either in Paris-Roubaix or along the country lanes I train on most? No! But for five or six watts I’d certainly risk them in a road race. Ultimately, we’d really like to see Parcours do similar testing with more all-around tyres like that new P-Zero.
There are other questions we don’t yet have answers to, including how relevant the Parcours yaw data is to the region in which you live and ride. Perhaps more problematic is the reliance on BicycleRollingResistance.com data. While BRR is a fantastic resource I’ve paid for myself, there are limitations to any testing. The limitations of roller drum testing mean that while the widely accepted BRR tyre ranking is representative of how tyres rank in the real world, the absolute rolling resistance numbers and deltas between tyres may change. What we don’t know is how any change in the delta between tyres could affect the combined ranking Parcours has created. A watt or two either way could alter the ranking.
There’s also the tyre pressures used. BRR tests at “Extra low” (54 PSI), “Low” (72 PSI), “Medium” (90 PSI), and “High” (108 PSI). Acknowledging the challenges in relying on a single PSI number, Dov Tate of Parcours explained they opted for BRR’s 72 PSI as it’s “closer to the pressure we’d recommend for this tyre size for most of our riders.”
Then we consider wind tunnel test speed. Parcours selected the industry-adopted 48 km/h benchmark. That is industry-standard and is also representative of the speeds a rider fitting a time trial tyre to a 68 mm deep rim might be hitting. Nevertheless, it’s not the speeds many of us hit all that often. There is an endless rabbit hole we could delve into debating the best speeds to test at and their relevancy to mere mortals: Do you pick the speed at which you most often sit in a group, or the speed you are when you’re winning races in a solo move? Ultimately, when wind tunnel time is limited, you have to pick a speed.
Parcours didn’t test at 30 km/h, but having done so previously with the same wheel and other tyres, it is confident scaling the results doesn’t change the overall ranking, even if it does change the differences between the tyres. Finally, while it’s beyond the scope of this test in particular, the data applies to tyres at only a single width.
Again, though, while it’s tempting to pick holes in the testing speeds, tyres chosen, reliance on third-party data, and even the rim dependency of the results, nevertheless, the results are fascinating, especially if you own a Parcours wheelset. We just wish more wheel brands would do the same, and Parcours could do the same again with more tyres.
The real benefit of this testing is less in the specific tyre listed as fastest; again, that’s going to depend on a host of variables as described above. But a framework for understanding what makes a particular tyre fast, in real-world conditions, has immense value for performance-minded riders.
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